README: remove username from IRC link

I don't know what on earth that berkus@ was doing there, the link didn't
work.
2 jobs for master in 8 minutes and 54 seconds
Status Name Job ID Coverage
  Build
passed build_clazy_clang_tidy #107764

00:05:24

passed linux kf5-qt5 qt5.15 #107763

00:03:29

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